The present invention relates to scanning electron microscope which is suitable for observing a minute pattern of the sample and at the same time measuring the length of the minute pattern of the sample such as semiconductor device.
In the general apparatus of the scanning electron microscope, the sample is not inclined and an electron beam irradiated from an electron source to the sample is inclined in a previously determined angle in order to observe the sample. When measuring the minute pattern of the sample, the electron beam is perpendicularly irradiated from the electron source which is disposed in vertical direction over the sample. Because, when the electron beam is inclined, the wave-form of secondary electron signal detected by the detector becomes non-symmetrical, and it becomes difficult to accurately measure the length of the pattern of the sample. Therefore, when measuring, the electron beam is perpendicularly irradiated. U.S. Pat. Nos. 4,670,652, 4,767,926, 4,751,384 are cited as examples of such device. In these conventional system, there arise following drawbacks.
When observing the sample, sometimes the electron beam is needed to be inclined, and when measuring the portion of the sample which is needed to be observed in some inclined angle, the sample is perpendicularly irradiated by moving the irradiation angle of the electron beam. And, the portion which is needed to be observed does not correspond to the portion which is needed to be measured, because the electron beam is irradiated with different angle in observing from that in measuring. Therefore, it is difficult to measure the portion of the sample which is needed to be observed with high accuracy.